Energy restriction dilutes the changes related to dietary fat type in membrane phospholipid fatty acid composition in rats

To investigate liver cell membrane phospholipid (PL) fatty acid (FA) compos ition in response to the consumption of different types of dietary fat and graded levels of energy intake, rats were fed for 10 weeks on a diet contai ning either fish oil, safflower oil, or beef tallow. Within each dietary fa t group, subgroups were either provided free access to food or energy-restr icted to 85% or 70% of the ad libitum intake by reducing the dietary carboh ydrate content while keeping other macronutrient intakes constant. Higher ( P < .05) proportions of docosahexaenoic acid, linoleic acid, and monounsatu rated FA were observed in the membrane PL of the fish oil, safflower oil, a nd beef tallow groups, respectively, resembling the FA composition in the d iets. However, such modifications of dietary FA composition in membrane PL FA were influenced by body energy status. The higher docosahexaenoic acid a nd total n-3 FA content in phosphatidylcholine (PC), sphingomyelin (SPH), a nd phosphatidylserine (PS) of the ad libitum fish oil group compared with t he other dietary groups no longer existed when energy supply was restricted . Therefore, reducing energy intake tended to dilute the changes of membran e PL FA composition occurring as a function of dietary FA composition. Thes e data suggest that the influence of dietary fat type on cellular structure and perhaps function becomes increasingly important with progressively pos itive energy balance. Copyright (C) 2000 by W.B. Saunders Company.